Multi-hull marine vessels such as catamaran sailboats and powerboats, with two hulls, and trimaran sailboats and powerboats, with three hulls, have been known in the art for a long period of time and have become very popular boats. Their popularity is, in part, because they are faster on a reach or a downwind run, they are more stable, and they are easier to sail than mono-hull boats. The larger trimarans are popular because of a large amount of upper deck space as compared to a similarly sized mono-hull boat.
However, the conventional catamarans and trimarans have significant drawbacks. A trimaran sailboat can be more difficult to sail upwind because it is a lighter weight vessel than a similarly sized mono-hull vessel, and the wind and waves coming at the trimaran will impede upwind travel. The superstructure of the trimaran can be subjected to very high forces when traveling upwind due to the vessel's cantilevered hulls. Trimarans are, however, very fast on a reach or on a downwind run. Mono-hull sailboats, on the other hand, have less superstructure that can cause excess windage when going to weather and that can cause large moment arm forces on the vessel. As a result, the mono-hull vessels are significantly more efficient at sailing upwind and have significant benefits in heavy weather windward sailing due to their ballast which allows the vessel to carry way even when hit with wind and waves.
Multi-hull vessels are typically less maneuverable, particularly at slow speeds, than mono-hull boats of similar size, because the multi-hull vessels have a substantially wider beam than the mono-hull vessels. Accordingly, maneuvering a trimaran in a tight area, such as is common in marinas and the like, is very difficult. The multi-hull vessels also encounter significant moorage and trailering problems because of the wide beam. It is often difficult to find a slip within a marina that has sufficient width to receive a wide vessel, and wide moorage slips are generally more expensive than narrow moorage slips. Trailering a wide beam vessel requires a suitable trailer, and such a trailer is generally more expensive than trailering a narrower boat.
Non-ballasted trimarans having been developed to avoid the problems of mooring or trailering a wide beamed vessel by providing folding outer amas that fold back or up relative to the center hull. However, these outer areas become non-structural members when they are folded back or up such that the folded trimaran is configured in a manner that is not suitable for sailing and is only suitable for mooring, storing, or trailering the vessel.
The wide beam of the conventional trimarans and catamarans provide high initial stability such that the multi-hull vessels are very stable when in the upright position and are very difficult to overturn and capsize or become inverted. Mono-hull vessels, in contrast, have a narrower beam and have a low initial stability such that it is easier for the mono-hull vessels to capsize or become inverted. Trimarans and catamarans do not have ballast in the hulls, so they have low ultimate stability and once the vessels begin to overturn, it is very difficult to prevent the vessels from overturning. In contrast, mono-hull vessels have substantial ballast in the keel, so as to provide high ultimate stability whereby the ballast will try to force the mono-hull vessel back to the upright position when the vessel begins to overturn.
A further drawback of the trimarans and catamarans is the fact that they are very difficult to right when the vessels do capsize or become inverted. As a result of the high initial stability, a trimaran or catamaran is just as stable in the inverted position as it is in the upright position. Thus, the high initial stability must be overcome before the vessel can be righted, and a significant amount of force must be exerted on the vessel in order to overcome the vessel's high initial stability. Unlike the multi-hull vessels, a mono-hull vessel is significantly easier to right because of the low initial stability due to the substantial ballast keel. The ballast keel typically has 25%-60% or more of the entire weight of the mono-hull vessel, such that, when the ballast keel lifts above the water, the ballast keel forces the mono-hull vessel to the upright position with the keel down. Accordingly, the ballast keel facilitates righting the mono-hull vessel once the low initial stability is overcome.
Although the conventional multi-hull vessels are difficult to right when overturned, a benefit of the multi-hull vessels is that the outer hulls will float when the vessel is inverted even if the center hull is completely flooded. In contrast, a ballasted mono-hull vessel, which is typically ballasted with lead or steel in the keel, will sink when it is capsized or inverted and the cabin becomes flooded.